1. Field of the Invention
This invention concerns a method for polishing rigid disks (which are used for computer hard drives) using an aqueous dispersion of fine abrasive particles. The aqueous dispersion may be incorporated into a chemical mechanical polishing slurry including at least one oxidizer and an optional catalyst. More particularly the method of this invention is especially adapted for polishing electroless nickel deposited rigid disks.
2. Description of the Related Art
Great strides are being made in the miniaturization of electronic components for the computer and electronics industries. Miniaturization has created component quality concerns, many of which are resolved by the precise polishing of computer and electronic substrate materials for magnetic disks and semi-conductors. As a result, identifying methods and compositions that can produce an essentially defect free surface has become crucial in the manufacture of computer and electronic substrates.
The driving force for miniaturization in rigid disks is similar to that in the semiconductor industry. Customers are demanding continually increasing storage capacity in rigid disks. At the same time the design rules used by computer manufacturers call for smaller hard drives. The only solution available to rigid disk manufacturers is to increase the storage density of the magnetic media. The recent development of magneto-resistive head technology allows heads to "float" at less that 50 nm above the disc surface at rotation rates in excess of 5000 rpm. Therefore a quantum leap is needed in surface finish quality of rigid disks as measured by such parameters as rms roughness and defectivity in order to enhance the signal to noise ratio of finished rigid disks.
Dispersions and chemical mechanical polishing (CMP) slurries have been developed for use in conjunction with semi-conductor device manufacture. However, few of the commercially available dispersions or CMP slurries have been evaluated in rigid disk polishing applications. For example, U.S. Pat. No. 4,475,981 discloses a composition for polishing the metal surface of nickel plated blanks for rigid memory disks with a composition including ceric oxide or aluminum oxide powder, a water soluble chlorine-containing mild oxidizing agent and an aqueous suspension of colloidal alumina oxide or ceria oxide. U.S. Pat. Nos. 4,696,697 and 4,769,046, each disclose methods for polishing memory disks using an abrasive composition including alpha-aluminum oxide and a polishing accelerator such as nickel sulfate. The aluminum oxide polishing agent preferably has a minum particle size of 0.7-4 .mu.m and a maximum particle size of 20 .mu.m or less. U.S. Pat. Nos. 4,915,710 and 4,929,257 each disclose abrasive compositions suitable for polishing aluminum based substrates for magnetic recording disks. The composition disclosed includes an alumina abrasive, a polishing accelerator such as gluconic or lactic acid and colloidal alumina. In addition, U.S. Pat. No. 5,527,423 discloses an abrasive composition that is particularly useful in the method of this invention. Likewise, U.S. patent application Ser. No. 08/753,482, incorporated herein by reference, discloses a chemical mechanical abrasive composition including an oxidizer and a catalyst that is useful in the method of this invention.
Methods for polishing rigid disks are disclosed in U.S. Pat. Nos. 4,769,046, 5,084,071, and 5,441,788. U.S. Pat. No. 4,769,046 discloses a method for polishing a layer of nickel plated on a rigid disk using a composition comprising aluminum oxide and a polishing accelerator such as nickel nitrate, aluminum nitrate, or mixtures thereof. U.S. Pat. No. 5,084,071 discloses a method of chemical mechanical polishing and electronic component using a composition including abrasive particles that are not alumina, a transition metal chelated salt, a solvent for the salt, and a small but effective amount of alumina. Finally, U.S. Pat. No. 5,441,788 discloses a method for manufacturing a nickel phosphor recording disk including polishing the NiP substrate to a surface roughness to no less than 2.0 nm RMS.
The commercially available rigid disk polishing slurries are unable to meet the new rigid disk surface finish parameters. Furthermore, compositions that are presently known to be capable of polishing rigid disks are unable to polish rigid disks at a high rate and, at the same time, produce an acceptable surface finish. Therefore, there remains a need for dispersions, and chemical mechanical polishing slurries that are capable of polishing rigid or hard disks at high rates with low defectivity, while providng a smooth surface finish.